This change makes a helper method for resetting connection handlers in
the Active Record tests. The change here is relatively small and may
seem unnecessary. The reason we're pushing this change is for upcoming
refactoring to connection management. This change will mean that we can
update one location instead of 9+ files to reset connections. It will
reduce the diff of our refactoring and make reusing this code easier in
the future.

The method name chosen is purposefully `clean_up_connection_handler`
over `clean_up_connection_handlers` because in the future there will
only be one handler.

Co-authored-by: John Crepezzi <john.crepezzi@gmail.com>